The present invention relates to improvements in die heads for forming different fibers from a common die, and more particularly to a die head assembly structure which forms two different fibers preferably in a melt-blown process.
In the melt-blown process microfibers of plastic are emitted from small die openings arranged in a row with the fibers attenuated by high velocity streams of air. Examples of this type of structure are shown in the copending applications of Langdon and Gerschon, Ser. No. 366,557, filed June 4, 1973 and Langdon, Ser. No. 463,460, filed Apr. 24, 1974, the disclosures of which are incorporated herein by reference in their entirety.
In the forming of a mat having fibers made by the melt-blown process, it is sometimes desirable to mix different polymers which have different physical characteristics. These different polymers may, in addition to having different physical characteristics in the filaments or threads that are finely formed, have different requirements for extrusion. That is, for optimum extrusion and attenuation, each may require delivery at a different pressure and may require that the plastic be at a different temperature. Each will have an optimum pressure and temperature, and possibly an optimum size extrusion opening to provide a filament which takes advantage of all the potential properties of the particular polymer. For providing a web which includes filaments of two different polymers, they should be formed simultaneously to obtain a mechanical entanglement and be formed so that the fibers are intermixed and positioned adjacent each other. Structures which heretofore operated under the melt-blowing process have been capable of providing at one time only a single polymer, and it has been necessary to provide a separate die head or to operate in a separate run to produce filaments from a second polymer having different characteristics.
It is accordingly an object of the present invention to provide a head construction for extrusion of filaments, preferably well adapted for use in the melt-blown process, which is capable of simultaneously forming plastic filaments from two different polymers.
A further object of the invention is to provide a head for use in a melt-blown process which has improved design features capable of producing two different polymers at their optimum temperature and wherein the production of each polymer does not interfere with or adversely effect the production of the other polymer.
A still further object of the invention is to provide a die head having improved construction characteristics which enables it to be relatively easily constructed and maintained and which is capable of producing simultaneously two different polymers in a melt-blown process and does not require excessive physical space so that it can operate efficiently and produce filaments in such a manner that they can readily be attenuated by high velocity air in accordance with the principles of the melt-blowing process.
Other objects, advantages and features, as well as equivalent structures which are intended to be covered herein, will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in the specification, claims, and drawings, in which: